Lithium air batteries have attracted great recent research interest due to their much higher energy density than that of the currently used Li-ion batteries (3600 Wh kg^-1 vs 300 Wh kg^-1). However, one of the most critical issues for practical application of Li-air batteries was the contamination of moisture and CO₂ from the air. Here we report a high performance O₂ selective mixed matrix membrane based on the metal organic framework (MOF) nanocrystallines of CAU-1-NH₂@PDA (CAU = Christian-Albrechts-University) and the polymer of polymethylmethacrylate (PMMA). CAU-1-NH₂ is a stable metal–organic framework [Al₄(OH)₂-(OCH₃)₄(H₂N-bdc)₃]·xH₂O, containing the new Al-containing octameric brick {Al₈(OH)₄(OCH₃)₈}¹²⁺. It has been found that the obtained mixed matrix membrane (MMM) possessed several advantages including high surface area, controlled porosity, adjustable chemical functionality, high affinity for specific gases and compatibility with polymer chains, making it attractive candidate for selective gas separation. Specifically, the functional group –NH₂ in the MOF, –OH in the polydopamine molecule, and the –C=O in the PMMA would preferably interact with CO₂ molecule. Also, the intrinsic hydrophobic behaviour of the PMMA polymer can favourably prevent the intrusion of moisture (Fig. 1). These two favourable effects guaranteed the Li-air cell working very stable under ambient atmosphere with very high relative humid (30%) by repelling CO₂ and moisture from the air. Evidently, the developed mixed matrix membrane based on CAU-1-NH₂@PDA and PMMA polymer opens the way to develop novel air-permeable membrane for real Li-air batteries applied in ambient conditions rather than in pure oxygen (Li-O₂) conditions.